Gasoline prices may have stabilized nationally for the past month, but in 14 states, they've already climbed to 15-month highs.

Nationally, regular unleaded gasoline averages about $3.66 a gallon, vs. $3.65 a month ago, according to price tracker gasbuddy.com. But prices in several Midwestern states have risen sharply on rising demand and the annual switch by refineries to costlier summer-blend fuels.

In Michigan, gas averages $3.96 a gallon, up 5% from $3.76 last month. Illinois motorists now pay an average $3.97 a gallon, up from $3.79 last month. In Wisconsin, gas now averages $3.74, up from $3.59. Minnesotans are paying an average $3.59 a gallon, vs. $3.50. Other states hitting 2014 highs:

Alaska ($4.04).

Oregon ($3.92).

Washington ($3.93).

Missouri, Wyoming ($3.50).

Nevada ($3.84).

New Mexico ($3.48).

North Dakota ($3.60).

Oklahoma ($3.46).

Arizona ($3.53).

Tom Kloza, senior energy analyst for pricetracker gasbuddy.com, expects national prices to top out at about $3.75 a gallon.

"That's higher than what we envisioned earlier this year, but it factors in the fear premium that is now reflected in crude oil prices,'' Kloza says.

Hawaii, averaging $4.36 a gallon, is the priciest state for gasoline. South Carolina, at $3.38 a gallon, is the cheapest.

Meanwhile, after an Iraq-fueled runup that propelled crude oil prices to nine-month highs last week, prices are mixed in Tuesday trading.

West Texas crude oil is off 68 cents to $106.22 a barrel, while Brent crude is up 61 cents to $113.55 a barrel following jumps of 4% last week. U.S. gasoline futures are up 1.7 cents to $3.09 a gallon.